Water clarification is well known throughout a number of industries. Various physical means have been used to remove particulate matter dispersed in a bulk liquid phase. Examples of common particulate separation techniques include filtration, settling, desalting, electrochemical techniques, centrifugation, flotation, and the like. Such separation processes can often be made more efficient by the use of coagulating and flocculating agents.
Coagulation may be defined as the stabilization of colloids by neutralizing the forces that keep the colloidal particles dispersed or separated from each other in the wastewater. Cationic coagulants are often used to provide positive electrical charges to the colloidal particles to neutralize the negative charge on the particles. As a result, the particles collide to form larger particles called flocs. Flocculation, on the other hand, refers to the action of polymeric treatments in the formation of bridges between the flocs to thereby form large agglomerates or clumps. Anionic and cationic polymers are commonly employed as flocculants to agglomerate the flocs so that the agglomerates will float and not settle. Once suspended in the wastewater, they can be removed via sedimentation, filtration, or other separation techniques.
Commonly employed cationic coagulants such as those based on polydiallyldimethylammonium chloride (PDADMAC) are disclosed for example in U.S. Pat. No. 3,288,770. Additionally, cationic copolymers such as those based on acrylamide copolymers with cationic repeat units such as quaternary ammonium acrylates dimethylaminoethylacrylate methyl chloride (AETAC) or dimethylaminoethylmethacrylate methyl chloride (METAC) are often used.
In those situations in which quaternary ammonium salt moieties are present in polymers that are employed as cationic coagulants, the anionic counter ion to the cationic nitrogen is often a chloride ion. These chloride ions are corrosive, and when excessive amounts of same are found in the wastewater, corrosion of metal surfaces in contact with the water can occur.
Additionally, environmentally based requests to limit the amount of total dissolved solids (TDS) present in effluents have been increasing over the years. Inorganic ions that are measured as part of the TDS discharge include chloride ions. Many industries and municipal wastewater facilities must comply then with new TDS standards; thus raising concern for chloride content in such discharge. TDS also presents an issue for water reuse of treated wastewater.